1. Field of the Invention
The present invention relates to abrasive jet machines used to cut or otherwise machine process various materials by generating a focused stream of fluid mixed with abrasive particles. The present invention relates in particular, to abrasive jet machines which use a pressurized liquid as the driving fluid to propel the abrasive particles for cutting or other machining operation.
The present invention is further related to an abrasive waterjet apparatus with a variable flow rate of an abrasive material to be entrained within the given fluid jet, wherein the flow rate is adaptively modulated to suit a particular operation of such apparatus.
Also, the present invention is related to an abrasive jet apparatus having an automatically controlled metering orifice for the abrasive dispenser, whereby flow rate of the abrasive material dispensed therethrough is adaptively regulated over a broad range of applications of the abrasive jet apparatus without operator intervention.
2. Prior Art
Abrasive waterjet cutting is a machining process where a focused ultrahigh velocity waterjet is used to accelerate abrasive particles which perform cutting. The high velocity waterjet is formed by pumping a fluid, such as for example, water to high pressure through a small diameter orifice. The resulting mixture of abrasive particles and water is discharged through a focusing tube as a high velocity composite jet to perform cutting or milling upon a workpiece.
In abrasive waterjet cutting, a water flow orifice restricts and accelerates the flow of high pressure water, typically at approximately 50 KSI to 65 KSI. This high speed jet of water is capable of cutting through various materials with relative ease. For metals, ceramics and other such materials, abrasives are added to the jet to increase the tribologic effect.
Abrasive waterjets typically employ a mini-hopper abrasive dispenser that is in turn fed by a large pressurized bulk hopper. Different sizes of abrasive materials (typically garnet having a mesh size within an approximate range of 80 to 220 mesh) are available for use with abrasive waterjets. An operator selects the abrasive size suitable for the material, thickness, finish, and other such parameters of the given workpiece, and sets the appropriate flow rate for the abrasive material which matches the size of the water flow orifice and focusing tube.
A typical abrasive waterjet apparatus 10 known in the art is illustrated in FIG. 1. The abrasive waterjet apparatus 10 includes a large pressurized bulk hopper 12 supplying an abrasive material to a mini-hopper abrasive dispenser 14. Presently known mini-hopper dispensers use a fixed or manually selectable metering orifice 16 such as a disk of preselected washer shape, or of manually adjustable aperture. A mechanical member 18 is used with the metering orifice 16 for occlusion against the flow of abrasive material therethrough. Typically, a pneumatic device such as a cylinder that responds to air pressure from a solenoid valve is used to actuate an abrasive valve mechanism 22 in this regard.
The abrasive material flow 20, having been regulated by the metering orifice 16 and admitted by the abrasive valve 22, freefalls until it meets an air jet 24. Shortly after passage by the abrasive valve 22, the abrasive material transitions from a freefall state to one of entrainment within a high speed air jet, forming an air/abrasive flow 26. The air/abrasive flow 26 is inducted into a waterjet mixing chamber 28 at a partial vacuum, and enters a mixing (or focusing) tube 30 where it contacts and mixes with the high speed waterjet. A highly focused abrasive/waterjet 32 is then expelled from the focusing tube 30 toward the workpiece 36 to be processed. Abrasive material size and flow rate are chosen in light of the specific operation to be performed upon that particular workpiece 36.
Note that the abrasive flow rate used for such machining operations as light material removal may not be sufficient for punching a hole or slicing through a thick section of the workpiece material. The operation may become overly time consuming, among other things. Conversely, a higher abrasive flow rate usually employed for cutting a thick section would not be appropriate for gently forming a delicate, sculptured shape. Presently known abrasive waterjet machines use either a fixed or manually selectable metering orifice that permits very limited control over the flow rate of the abrasive material, thus preventing optimal adaptation of the abrasive material flow rate, much less precise active control thereof. There is a need in the art, therefore, for a system and method whereby the mass flow rate of an abrasive material may be simply yet accurately adapted for assorted abrasive jet machining operations.